Core Losses ($W_i$ or $P_i$): Occur in the iron core due to AC and frequency. Constant loss.
- Eddy Current Losses ($W_e$ or $P_e$): Due to circulating currents in laminated core.
  - $W_e = K_e B_{m}^2 f^2 t^2 V$ (Steinmetz empirical formula)
  - Minimized by thin, insulated laminations.
- Hysteresis Losses ($W_h$ or $P_h$): Due to magnetization cycles.
  - $W_h = K_h B_{m}^{1.6} f V$
  - Minimized by proper magnetic material.
Copper Losses ($W_{cu}$ or $P_{cu}$): Occur in primary ($R_1$) and secondary ($R_2$) windings. Variable loss.
- $W_{cu} = I_1^2 R_1 + I_2^2 R_2$
- In terms of equivalent resistance: $W_{cu} = I_1^2 R_{01} = I_2^2 R_{02}$
- $R_{01} = R_1 + \frac{R_2}{K^2}$, $R_{02} = R_2 + R_1 K^2$
- Minimized by low resistance windings.
Total Losses: $W_{total} = W_i + W_{cu}$

$\eta = \frac{\text{Output Power}}{\text{Input Power}} = \frac{P_{out}}{P_{in}} = \frac{P_{out}}{P_{out} + W_{total}}$
$\eta = \frac{V_2 I_2 \cos\phi_2}{V_2 I_2 \cos\phi_2 + P_i + P_{cu}}$
For fractional load $n$ (or $x$):
- New copper loss $P'_{cu} = n^2 P_{cu, F.L.}$
- $\eta = \frac{n \cdot (\text{VA rating}) \cos\phi}{n \cdot (\text{VA rating}) \cos\phi + P_i + n^2 P_{cu, F.L.}}$
Condition for Maximum Efficiency: Iron Loss = Copper Loss ($P_i = P_{cu}$)
Load current at maximum efficiency: $I_{2m} = I_{2,F.L.} \sqrt{\frac{W_i}{W_{cu}}}$

A three-phase AC motor widely used in industrial applications.
Advantages: Simple, rugged, low cost, high reliability, high efficiency, good power factor, low maintenance. Small IMs are self-starting.
Disadvantages: Constant speed motor (speed not easily varied), lower starting torque compared to DC shunt motor.

Stator:
- Steel frame with hollow cylindrical core of thin silicon steel laminations.
- Stator conductors in insulated slots, connected in balanced three-phase star or delta.
- Wound for a definite number of poles.
- Synchronous speed: $N_s = \frac{120f}{P}$ (rpm), where $f$ is frequency, $P$ is number of poles.
- Applying 3-phase AC supply produces a rotating magnetic field (RMF) at synchronous speed.
Rotor: Rotating part, mounted on shaft. Two types:
- Squirrel Cage Rotor:
  - Cylindrical laminated core with slots for rotor windings (heavy copper/aluminum bars).
  - Bars welded to end rings, short-circuiting both ends.
  - Slots are skewed to reduce noise and locking tendency.